A few questions:
How long have you had your bags?
Do you store them stuffed?
Do you carry them full?
Mine (oxblood w. strap) does not slouch like that, but I could see if you didn't stuff the bag fully when you stored it the leather naturally tending to crease like that due to the weight of the top flap.
Crap. The green I've had a year and the aubergine only a few months but I'm the second owner and I received it this way. I do not store them stuffed and I carry a decent amount but never full. I guess I need to start storing them stuffed, although it may be a lost cause. It's so ANNOYING that they slouch.